The present invention relates to a wafer stage mainly used for manufacturing a semiconductor device, and particularly to a wafer stage suitably used for a plasma process performed in a state in which a wafer is heated at a high temperature of 400.degree. C. or more.
In the field of manufacture of semiconductor devices, there are known a variety of plasma processes for wafers, such as plasma etching and plasma CVD.
In such a plasma process, particularly, in plasma etching, there is a tendency to adopt low temperature etching for increasing a processing accuracy. As is apparent from this viewpoint, the temperature control for wafers is being regarded important.
In recent years, with the advance of multi-level interconnection technology for LSIs, there has been strong demands toward development for a new interconnection material such as copper for reducing the resistance of the interconnection and toward adoption of high density plasma CVD for gap filling technology. As a result, a plasma process performed at a high temperature is being regarded important, in addition to the above-described plasma process performed at a low temperature.
In such a plasma process performed at a high temperature, however, a wafer receives a large heat input due to generation of plasma upon ion bombardment at an etching step or upon irradiation of high density plasma at a gap filling step by CVD or a barrier metal formation step by CVD. Consequently, the temperature of the wafer is possibly increased about 40 to 100.degree. C. or more as compared with that before generation of plasma.
Accordingly, in the plasma process performed at a high temperature in which a wafer is heated by a wafer stage holding the wafer, it becomes important to suppress the effect of heat input due to generation of plasma on the wafer and to control the temperature of the wafer at a setting value.
In the related art, however, the temperature control for a wafer has not been sufficiently performed at a high temperature, and from the practical standpoint, the process condition has been set such that the temperature of a wafer stage is previously set at a lower value in consideration of the above-described temperature rise caused during processing.
The reasons why it is difficult to control the temperature of a wafer in a plasma process performed at a high temperature are as follows:
(1) The heating of a wafer by a wafer stage is generally performed using a heater provided in the wafer stage; however, a temperature rise of the wafer caused by heat input due to generation of plasma cannot be suppressed only by heating using the heater. PA1 (2) In the case using a wafer stage including an electrostatic chuck for attracting a wafer and a metal made jacket for adjusting the temperature of the electrostatic chuck, although the improvement in the degree of bonding between a wafer and a wafer stage has been examined, an electrostatically chucking technology for improving the temperature-controllability for the wafer has been not established.
In particular, with respect to the item (2), at a high temperature, an organic material based film made from polyimide or the like cannot be used as a dielectric member for an electrostatic chuck, and a ceramic material is difficult to use because of the variable bulk resistivity thereof. Also, a ceramic material presents another problem in terms of the joint with a metal material in an electrostatic chuck or a metal made jacket.
In general, a ceramic material has a linear thermal expansion coefficient largely different from that of a metal, and consequently, when such a ceramic material is joined to a metal by thermal spraying or brazing, it tends to be broken in a heating condition due to a difference in linear thermal expansion coefficient therebetween. In particular, when the temperature of a wafer is set at 400.degree. C. or more upon a plasma CVD process, even in the case of using an Al made jacket, since there is a large difference in linear thermal expansion coefficient between an electrostatic chuck and the Al made jacket, it becomes difficult to prevent breakage of the electrostatic chuck and hence to direct join them to each other.